Object-proximity monitoring and alarm system

ABSTRACT

A weight-sensitive mat or other sensor determines whether a child seat in a vehicle is occupied, a transmitter is proximate to the sensor, and a keychain fob or other portable unit includes a receiver and an alarm. Generally, if the child seat is occupied and the keychain fob is removed from proximity to the transmitter, the transmitter communicates this to the keychain fob receiver and the alarm is activated. Exemplary embodiments include an add-on kit including a base unit with a transceiver for use with existing car seats having a base and a detachable shell, an add-on kit without the base unit for use with existing unitary car seats, and a car seat with the child sensor, transmitter, and/or base unit built into it.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of U.S. Provisional PatentApplication Ser. No. 60/325,852 filed Sep. 28, 2001, which is herebyincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates generally to alarm systems for monitoringthe proximity of objects and, more particularly, to a system formonitoring the proximity of a child and alerting a parent leaving avehicle when a child remains in a child seat in the vehicle.

BACKGROUND OF THE INVENTION

Infant car seats are commonly used for safely restraining children whenthey are driven in motor vehicles. Because of the increased safety theyprovide, car seat use is now mandated in most, if not all, of the UnitedStates. As a result, injuries to infants involved in automobileaccidents have decreased over the years.

On occasion, however, using a car seat has resulted in another type ofinjury to infants. With their child restrained in a rear-facing car seatin the back seat of the car, and with parents busier and morepreoccupied than ever, even the most attentive parents couldaccidentally leave their vehicle while their sleeping child remains inthe car seat. The unintentionally abandoned child is then subject toinjury from choking, asphyxiation, hyper- or hypothermia, etc. In fact,there have been a disturbingly large number of cases over the last fewyears of children dying after being accidentally left unattended for toolong in their parent's vehicles. By one estimate, more than 150 childrendied between 1996 and 2001 because they were left in cars unattended.

There are no known devices that satisfactorily overcome this deficiencyin the use of conventional car seats. Known car seat-related safetydevices include systems for monitoring when the vehicle ignition hasbeen turned off with a child in the car seat in the vehicle, monitoringmotion or temperature in the parked vehicle, and monitoring whether thecar seat is properly installed. Other known devices include childposition and presence monitors. None of these devices, however, haveadequately solved the aforementioned problem.

Accordingly, it can be seen that a need remains for a car seat-relatedsafety system that eliminates or at least reduces the likelihood of aparent of other attendant accidentally leaving a vehicle while a childremains in the car seat in the vehicle. In particular, there is neededsuch a system that warns a parent when unintentionally leaving the childin the car. Additionally, there is needed such a car seat safety systemthat can be used with existing car seats and one that can bemanufactured into new car seats. Furthermore, a need exists for such acar seat safety system that is cost and time efficient to manufacture,install, and use. It is to the provision of a safety system meetingthese and other needs that the present invention is primarily directed.

SUMMARY OF THE INVENTION

Generally described, the present invention includes an object-proximitymonitoring and alarm system for use with an object carrier. Forillustration purposes, the system will be described for use with a childseat securable in a vehicle, though it may be used with strollers orother child carriers. In the child car seat application, the systemoperates to alert a caretaker if he or she leaves the proximity of avehicle while the child seat is occupied.

The system includes at least one sensor that determines whether thechild seat is occupied, a main transmitter mounted to or in proximity tothe child seat, and a portable unit including a receiver and an alarm.The transmitter indicates to the portable unit receiver that the childseat is occupied, as determined by the sensor. If the portable unit isremoved from the proximity of the transmitter at a time in which thesensor detects that the seat is occupied, then the portable unit alarmis activated.

In a first exemplary embodiment of the invention, the sensor is providedby a weight-sensitive mat. The mat is placed on top of the seat portionof the child seat or otherwise positioned for sensing the weight of achild. Alternatively, the sensor can be provided by other devices forsensing the presence of a child in the child seat, such a infraredsensors, radio frequency detection devices (e.g., RADAR), photocells,and so forth.

The portable unit is provided by a keychain fob housing the alarm andthe receiver. In this way, when a driver leaves the proximity of thevehicle while carrying the fob, the alarm may be activated. The alarmcan include a speaker, a light, a vibrator, a combination of these, oranother type of alarm mechanism. And the portable unit may be providedin another form such as embedded in a watch or other jewelry, a card orother structure that can be carried in a wallet, a panel with anadhesive side for attaching to an existing keychain fob, and so forth.

The system is configured for the main transmitter to indicate to thereceiver when the alarm is to be activated. In one example, thetransmitter operates to intermittently transmit a first electromagneticsignal if the child seat is occupied and a second electromagnetic if thechild seat ceases to be occupied. The determination of whether the childseat is occupied is made by the sensor. The portable unit receives thefirst and second electromagnetic signals and, unless one of the secondelectromagnetic signals is received in the interim, activates the alarmif more than a predetermined length of time passes between successivereceptions of the first electromagnetic signal. Also, the first andsecond signals have a strength that can be received by the portable unitreceiver only within a predetermined range. In this way, if a personcarrying the fob leaves the proximity of the vehicle while the childseat is occupied, the alarm is activated. Of course, the system can beconfigured in other ways to accomplish this intended function.

For use with two-piece child seats having a base and a detachable shell,the system may include a base unit mountable to or in proximity to thebase and an object detector assembly mountable to or in proximity to theshell. The base unit includes a transceiver comprising the maintransmitter and a second receiver, and the object detector assemblyincludes the sensor and a second transmitter. The object detectorassembly includes the sensor and a second transmitter. The secondtransmitter of the object detector assembly indicates to the secondreceiver of the base unit transceiver if the child carrier is occupied,as determined by the sensor. For example, the second transmitter may beconfigured to transmit a third electromagnetic signal to the base unittransceiver if the child carrier is occupied, and the base unittransceiver configured to transmit the first electromagnetic signal onlyif the third signal is being received. In this way, the car seat basecan be left in the vehicle while the shell is removed for carrying thechild or for mounting to a base in another car, without activating thealarm.

In the first exemplary embodiment just described, the system may beprovided as an add-on kit for use with an existing child seat. Toinstall the system, the sensor mat is placed on the seat portion of thechild seat, the transmitter is mounted to or in the proximity of thechild seat, and the keychain fob is connected to the user's keychain.The transmitter may be mounted to the child seat base by hook-and-loopfasteners, adhesive strips, screws, or other conventional fasteners, tothe vehicle sun visor by a clip or other conventional fastener, or toanother component of the vehicle of child seat.

In a second exemplary embodiment of the present invention, the system isarranged for use with a unitary child seat. In this embodiment, there isno need for an indication of whether the shell is mounted to the basebecause it is not detachable. So the transmitter is provided without thesecond receiver, that is, a transmitter is provided instead of atransceiver. And the sensor is provided without the second transmitterof the object detector assembly.

For any of these or other embodiments of the invention, the detectorassembly, the base unit, and the keychain fob can be provided separatelyas replacement parts for use with an existing system. In this way, if aperson loses his or her keys or damages the base unit, or if the infantrepeatedly soils the sensor mat, then the user can purchase only theneeded replacement component.

In a third exemplary embodiment of the present invention, the system isarranged to be made and sold integrally with the child seat. In thisembodiment, the sensor mat is built into the seat portion of the childseat, or otherwise positioned. Similarly, the transmitter may be builtinto the base or shell, or included in an object detector assembly withthe senor, so that it is not obtrusive.

In a fourth exemplary embodiment, the system includes a sensor providedby a switch configured for determining if a seat belt of the child seatis connected. And in a fifth exemplary embodiment for two-piece childseats, a second sensor can be provided for determining if the shell ismounted to the base and deactivating the system if the shell is detachedfrom the base.

Accordingly, the present invention includes a child-proximity monitoringand alarm system that notifies a parent or other caretaker when about tounintentionally leave a child in a vehicle. Advantageously, the systemcan be provided as an add-on kit for use with an existing child car seator it can be built into and provided with a new child seat. In addition,the system can be provided for use with two-piece car seats so that itallows the detachable shell to be removed from the base without settingoff the alarm, or it can be provided for use with unitary child seats.Furthermore, the invention includes a portable unit such as a keychainfob and a base unit, each of which can be provided separately as new orreplacement parts. Moreover, the various forms of the invention areefficient to manufacture, install, and use, so that they are affordable,reliable, and easy-to-use for average consumers.

These and other features and advantages of the present invention willbecome more apparent upon reading the following description inconjunction with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a schematic diagram of a child-proximity monitoring and alarmsystem according to a first exemplary embodiment of the invention,showing an object detector assembly on a vehicle child seat, a base uniton a vehicle sun visor, and a keychain fob.

FIG. 2 is a perspective view of the detector assembly of FIG. 1, showinga transmitter and a sensor provided by a weight-sensitive mat.

FIG. 3 is a perspective view of the base unit of FIG. 1, showing ahousing for a transceiver.

FIG. 4 is a perspective view of the keychain fob of FIG. 1, showing ahousing for a receiver and an alarm.

FIG. 5 is a block diagram of the detector assembly of FIGS. 1 and 2.

FIG. 6 is a flow diagram of the operation of the detector assembly ofFIG. 5.

FIG. 7 is a block diagram of the base unit of FIGS. 1 and 3.

FIG. 8 is a flow diagram of the operation of the base unit of FIG. 7.

FIG. 9 is a block diagram of the keychain fob of FIGS. 1 and 4.

FIG. 10 is a flow diagram of the operation of the keychain fob of FIG.9.

FIG. 11 is a schematic diagram of a child-proximity monitoring and alarmsystem according to a second exemplary embodiment for use with a unitarychild seat, showing a detector assembly on the child seat and a keychainfob.

FIG. 12 is a schematic diagram of a child-proximity monitoring and alarmsystem according to a third exemplary embodiment that is integrallyprovided with a child seat, showing the detector assembly and the baseunit integrally provided with the child seat.

FIG. 13A is a front view of a portion of a fourth exemplary embodimentsimilar to the system of FIG. 12, showing the sensor provided by aswitch for detecting whether the seat belt of the child seat isconnected.

FIG. 13B is a side view of the portion of the sensor of the system ofFIG. 13A.

FIG. 14 is a side view of a portion of a fifth exemplary embodiment foruse with two-piece child seats, showing a second sensor for detectingwhether the child seat shell is mounted to its base.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Referring now to the drawing figures, wherein like reference numeralsrepresent like parts throughout the several views, the present inventionincludes an object-proximity monitoring and alarm system for use withobject carriers. The system can be used with child car seats, strollers,cribs, child bicycle seats, or other child carriers. For purposes ofillustrating its features and benefits, however, several exemplaryembodiments of the system are described herein in use with vehicle childseats. In these embodiments, the system warns a caretaker if he or sheleaves the proximity of a vehicle while a child is still in a car seatin the vehicle.

FIGS. 1-10 illustrate a first exemplary embodiment of the presentinvention, referred to generally as the system 10. As shown in FIGS.1-4, the system 10 includes a detector assembly 20, a base unit 30, anda portable unit 40. The detector assembly 20 is placed upon, mounted to,built into, or otherwise arranged to determine whether a child seat 12on a seat 14 in a vehicle is occupied. The base unit 30 is mounted to adriver's side sun visor 16 of the vehicle, mounted to or built into thechild seat itself, or otherwise arranged to receive transmissions fromthe detector assembly 20. And the portable unit 40 is carried by thecaretaker of the child and receives transmissions from the base unit 30.

The detector assembly 20 includes at least one sensor 22 that determineswhether the child seat is occupied and transmits a firstproximity-sensitive indication when the child seat is occupied. The baseunit 30 receives the first proximity-sensitive indication when the childseat is occupied and, in response, relays a second proximity-sensitiveindication that the child seat is occupied. The portable unit 40includes an alarm 44, receives the second proximity-sensitive indicationthat the child seat is occupied, and, in response, alerts the user ifthe portable unit is removed from proximity to the base unit.

The detector assembly 20 transmits the first proximity-sensitiveindication with a strength so that it can only be received by the baseunit 30 within a first predetermined proximity range. And the base unit30 transmits the second proximity-sensitive indication with a strengthso that it can only be received by the portable unit 40 within a secondpredetermined proximity range. For example, in a typical commercialembodiment the first predetermined proximity range is about 2-3 metersand the second predetermined proximity range is about 5-10 meters.

In this configuration, the system 10 can be provided as an add-on kitfor use with a two-piece child seat having a base and a detachableshell. If the shell of the child seat is removed from the base fartherthan the first predetermined proximity range, then the portable unitalarm will not activate. So the user can remove the shell to carry thechild around and/or install the shell on the base in another vehiclewithout activating the alarm. Or the system can be used with a unitarychild seat so that it can be removed from a vehicle without activatingthe alarm.

Referring to FIGS. 1 and 2, the detector assembly sensor 22 is providedby a weight-sensitive liner mat. Such mats are known in the art andsometimes used as training devices for pets. One known pet trainingdevice is the commercially available SOFA SCRAM mat that is placed on asofa and that beeps shrilly when a pet jumps up onto mat, therebydissuading pets from getting up on furniture. In the detector assemblysensor 22, the sensor mat 22 is sized and shaped to fit onto the seatportion of the child seat 12. For example, in a typical commercialembodiment the mat is generally rectangular and about 30×30×1 cm. Themat can be made of a variety of materials, but preferably it issufficiently flexible that it will fit onto most or all existing childseats and it has an outer lining made of a non-porous material thatprotects against spills. Also, in order to keep the mat secured in placeon the child seat 12, it can be provided with hook-and-loop fasteners,straps, snaps, or other conventional fasteners.

Alternatively, the sensor 22 can be provided by other devices forsensing the presence of a child in the child seat 12. For example, thesensor can be provided by infrared sensors or photocells in combinationwith a light source that is blocked upon the child sitting in the seat,radio frequency detection devices such as RADAR, and/or other devicesfor sensing the presence of the child by means such as pressure,capacitance, conductance, temperature, etc. Or the aforementionedweight-sensitive mat can be sized and shaped for fitting under andsupporting the weight of the entire child seat or of the detachableshell of the child seat.

In addition to the sensor 22, the detector assembly 20 includes acommunication and control system for communicating with the base unit30, the components and operation of which are described in detail withreference to FIGS. 5 and 6. The communication and control system isenclosed in a housing 24 which may have an alarm speaker 26 and one ormore indicator lights 28. Preferably, the housing 24 is flat and thinand attached to the sensor 22 at an unobtrusive location. For example,in a typical commercial embodiment the housing 24 is about 3×3×1 cm,about the same thickness as the sensor mat 22. Or the housing 24 can beprovided separately and connected to the sensor 22 by wires, or it canbe otherwise sized and shaped, if so desired.

Referring to FIGS. 1 and 3, the base unit 30 includes a communicationand control system for communicating with the detector assembly 20 andthe portable unit 40, the components and operation of which aredescribed in detail with reference to FIGS. 7 and 8. The system isenclosed in a housing 32 which may have an alarm speaker 34 and one ormore indicator lights 36 similar to those of the detector assembly 20.Also, the housing 32 may have a clip 38 for removably attaching the baseunit 30 to a vehicle sun visor, or it may be provided with adhesivestrips, screws, straps, or other fasteners for attaching it to the childseat or another part of the vehicle. In a typical commercial embodimentthe base unit 30 is about 5×5×1 cm.

Referring to FIGS. 1 and 4, the portable unit 40 is provided by akeychain fob for attachment to a keychain ring carrying keys. The fob 40includes a housing 42 which may have an alarm speaker 44 and one or moreindicator lights 46 similar to those of the detector assembly 20 and/orthe base unit 30. In addition, the fob 40 has a disable switch 48 formanually disabling the system 10. And the fob housing 42 encloses acommunication and control system for communicating with the base unit30, the components and operation of which are described in detail withreference to FIGS. 9 and 10. The alarms 44 can include a speaker, aflashing light, a vibrator, a combination of these, or another type ofalarm. In a typical commercial embodiment the fob housing 42 is about5×5×1 cm.

Alternatively, the portable unit 40 may be embodied in other forms. Forexample, the components of the portable unit 40 can be embedded in awatch, other jewelry, a smart card, another structure that can becarried in a wallet, or a cell phone, personal digital assistant, orother portable electronic device. Or the portable unit 40 may beprovided by a panel with an adhesive side for attaching to an existingkeychain fob.

Turning now to FIGS. 5-10, the structure and operation of thecommunication and control systems for the detector assembly 20, the baseunit 30, and the portable unit 40 will now be described. Thesecomponents communicate by short-range wireless signals such as radiofrequency (RF) signals using wireless communications software such asBLUETOOTH. The RF signals are broadcast as pulses of time chosen toaccommodate the battery needs and information required. Each RF signalhas a carrier wave modulated by an information signal. The modulationtype could include frequency modulation (FM), amplitude modulation (AM),and phase modulation (IQ). Other modulation schemes are possible andlimited only to practical considerations.

In the information transmission scheme of the first exemplaryembodiment, each pulse contains sufficient bits of information (upondemodulation and analog-to-digital conversion) to indicate “monitoringsignal 1” (S1) or “disable signal 2” (S2) transmitted from the base unit30 and “active signal 3” (S3) transmitted from the detector assembly 20(see FIG. 1), and a number of bits which comprise a “privacy code”. Theprivacy code is assigned to each transmitter-receiver pair. Additionalencoding could also include error checking and redundant bits forinterference tolerance.

FIG. 5 shows the communication and control system 500 for the detectorassembly 20. The detector assembly 20 sends to the base unit 30 thefirst proximity-sensitive indication that the sensor 22 is activated bya child in the car seat 12. This indication may be provided by a varietyof different systems 500 implementing a variety of different indicationschemes.

In the first exemplary embodiment, the communication and control system500 includes the sensor 22, a microcontroller 502, a transmitter 504, anantenna 506, and various output and power supply components. The outputand power supply components include the acoustic transducer 26 such asan alarm speaker or piezoelectric buzzer, the indicator lights such asLEDs 28, amplifiers 512 for the acoustic transducer 26 and the LEDs 28,a primary power source 514 such as one or more batteries, a backup powersource 516 such as one or more batteries, and a low battery detectioncircuit (LBDC) 518.

The sensor 22 senses the presence of a child in the car seat andproduces a logical voltage that can be interpreted by themicrocontroller 502 to indicate the presence or absence of the child.The microcontroller 502 implements the combinational and sequentialfunctions that control the timing and states of the output components(e.g., transmitter 504, alarm 26, LEDs 28, etc.) based on the inputcomponents (e.g., sensor 22, LBDC 518, etc.). Depending on thecapability of available sensors, the microcontroller may not be neededfor the detector assembly 20.

The transmitter 504 converts the logical voltages from themicrocontroller 502 to modulated, analog, active signal S3, which istransmitted on the antenna 506. The transmitter 504 transmits the activesignal S3 to the base unit 30 over a first predetermined proximity rangeof a short distance, for example, 2-3 meters, if and only if the childis detected by the sensor 22 in the car seat.

In addition, the microcontroller 502 sends electrical signals to theacoustic transducer 26, the LED indicator lights 28, and/or other outputcomponents. The acoustic transducer 26 converts the electrical signal toan audible sound and the LED indicator lights 28 are illuminated whenactivated. Amplifiers 512 are provided, if needed, to convert (buffer) alow-power logical signal to a powered signal sufficient to drive thealarm speaker 26 or the LEDs 28. Upon receiving an electrical signalfrom the microcontroller 502, one of the LEDs 28 indicates the off-state(LED off), on-state (LED on), and low battery state (LED blinking). Uponreceiving another electrical signal from the microcontroller 502, thealarm speaker 26 sounds to indicate that the batteries are low.

The primary battery 514 delivers power to all active components exceptthe LBDC 518, which is powered by the backup battery 516. The batteries514 and 516 may be consist of single or multiple power cells in seriesor parallel, may be provided by conventional AA, D-cell, or otherbatteries, depending on operational lifetime and power requirements. Inthis embodiment, the power requirements are based on a low power RFtransmission (e.g., <10 mW), and very low standby current (e.g., <1 mA).In addition, the LBDC 518 measures the power (e.g., via voltage)remaining in the primary battery 514 and outputs a logical value to themicrocontroller 502 to indicate if the battery voltage is above or belowa predefined “low battery” threshold voltage. If the primary battery is“low” then the microcontroller 502 sends the signals to sound thespeaker alarm 26 and to blink the LED 514, as described above. Thebackup batteries 516 can then be used to operate the system 500,allowing some time for the user to replace or recharge the batteries 514and 516.

Referring additionally to FIG. 6, there is shown the operational processflow 600 of the communication and control system 500 of the detectorassembly 20. At 602, in the standby mode, the system 500 consumesminimal power and transmits no signals. In this state, at 604, thedetector assembly 20 checks for the presence of a child in the car seat12. If a child is detected, the transmission sequence begins, if not,the standby loop continues.

At 606, the transmission sequence begins. First, one of the LEDindicators 28 is turned on. The state of the indicator light 28 (steadyor blinking) is determined by the LBDC 518 and is controlled by themicrocontroller 502. Then at 608, the LBDC 518 checks to see if theprimary battery 514 has fallen below the acceptable voltage threshold.If it has, the alarm sequence is initiated at 614, if not, thetransmission sequence continues. Next, at 610 the short-range activesignal S3 is transmitted over the first predetermined proximity range.If the sensor 22 continues to detect the child, the signal S3transmission loop continues, but if not, then the transmission sequenceis ended at 618.

If at 608 the LBDC 518 determined that the primary battery 514 power waslow, then at 614 the alarm sequence is initiated. In the alarm sequence,the alarm 26 is turned on, then at 616 the LBDC 518 rechecks the voltageof the primary batteries 514. If the primary batteries 514 have beenreplaced or recharged so that the voltage is now above the minimumacceptable threshold, then the alarm 26 is turned off and the alarmsequence is ended at 618. If not, then the alarm loop continues.

Upon the termination of the transmission sequence from 612, and upon thetermination of the alarm sequence from 616 (if it was activated), theLED indicator 28 is turned off and the system 500 is returned to thestandby loop at 602. The operational process flow 600 of the system 500continues in this way, awaiting the next time a child is sensed in thecar seat 12.

FIG. 7 shows the communication and control system 700 for the base unit30. The base unit 30 receives from the detector assembly 20 the firstproximity-sensitive indication that the sensor 22 is activated by achild in the car seat 12, but only receives the first indication whenthe base unit 30 and the detector assembly 20 are close together withinthe first predetermined proximity range. Then the base unit 30 transmitsa second proximity-sensitive indication to the portable unit 40 that thesensor 22 is activated by a child in the car seat 12, but only sends thesecond indication when the first indication is being received from thedetector assembly 20. This second indication may be provided by avariety of different systems 700 implementing a variety of differentindication schemes.

In the first exemplary embodiment, the communication and control system700 includes a microcontroller 702, a transceiver 704, an antenna 706,and various output and power supply components. The output and powersupply components include the acoustic transducer 34 such as an alarmspeaker or piezoelectric buzzer, the indicator lights such as LEDs 36,amplifiers 712 for the acoustic transducer 34 and the LEDs 36, a primarypower source 714 such as one or more batteries, a backup power source716 such as one or more batteries, and a low battery detection circuit(LBDC) 718.

The microcontroller 702 implements the combinational and sequentialfunctions that control the timing and states of the output components(e.g., transceiver 704, alarm 34, LEDs 36, etc.) based on the inputcomponents (e.g., transceiver 704, LBDC 718, etc.). The transceiver 704converts the modulated, analog, low-magnitude active signal S3 receivedfrom the detector assembly transmitter 504 to demodulated, buffered,logical voltage signals read by the microcontroller 702, and convertslogical voltages from the microcontroller 702 to modulated monitoringand disable signals S1 and S2 to be transmitted on the antenna 706. Thetransceiver 704 transmits the monitoring signal S1 to the portable unit40 over a second predetermined proximity range of a medium distance, forexample, 5-10 meters, if and only if the child is detected by the sensor22 in the car seat 12 and the base unit 40 and the detector assembly 20are within the first predetermined proximity range. If the base unit 40and the detector assembly 20 are not within the first predeterminedproximity range and/or the child is no longer detected by the sensor 22in the car seat 12 so that the base unit transceiver 704 does notreceive the active signal S3, then the transceiver 704 transmits thedisable signal S2 to the portable unit 40. It will be understood thatthe transceiver 704 may be provided by a conventional receiver andtransmitter, by a conventional transceiver with shared components suchas the antenna, or otherwise.

In addition, the microcontroller 702 sends electrical signals to theacoustic transducer 34, the LED indicator lights 36, and/or other outputcomponents. The acoustic transducer 34 converts the electrical signal toan audible sound and the LED indicator lights 36 are illuminated whenactivated. Amplifiers 712 are provided, if needed, to convert (buffer) alow-power logical signal to a powered signal sufficient to drive thealarm speaker 34 or the LEDs 36. Upon receiving an electrical signalfrom the microcontroller 702, one of the LEDs 36 indicates the off-state(LED off), on-state (LED on), and low battery state (LED blinking). Uponreceiving another electrical signal from the microcontroller 702, thealarm speaker 34 sounds to indicate that the batteries are low.

The primary battery 714 delivers power to all active components exceptthe LBDC 718, which is powered by the backup battery 716. The batteries714 and 716 may consist of single or multiple power cells in series orparallel, may be provided by conventional AA, D-cell, or otherbatteries, depending on operational lifetime and power requirements.Alternatively, the base unit may be provided with a cord and jack forconnecting to the cigarette lighter socket and running off the vehicle's12 vDC power system. In the present embodiment, the power requirementsare based on a medium power RF transmission (e.g., <100 mW), and verylow standby current (<1 mA). To improve battery efficiency, the firstand second signals S1 and S2 may be transmitted as pulses (e.g., <1 s)at intervals (e.g., 1-2 minutes apart).

In addition, the LBDC 718 measures the power (e.g., via voltage)remaining in the primary battery 714 and outputs a logical value to themicrocontroller 702 to indicate if the battery voltage is above or belowa predefined “low battery” threshold voltage. If the primary battery is“low” then the microcontroller 702 sends the signals to sound thespeaker alarm 34 and to blink the LED 36, as described above. The backupbatteries 716 can then be used to operate the system 700, allowing sometime for the user to replace or recharge the batteries 714 and 716.

Referring additionally to FIG. 8, there is shown the operational processflow 800 of the communication and control system 700 of the base unit30. At 802, in standby mode, the system 700 consumes minimal power andtransmits no signals. In this state, at 804, the microcontroller 702checks for T1=1. If the active signal S3 is received by the transceiver704 from the detector assembly transmitter 504, logical bit T1 is set to“1.” If this occurs, the base unit 30 is enabled and the transmissionsequence begins. If not, then the standby loop continues.

At 806, the transmission sequence begins. First, one of the LEDindicators 36 is turned on. The state of the indicator light 36 (steadyor blinking) is determined by the LBDC 718 and is controlled by themicrocontroller 702. Then at 808, the transceiver 704 beginstransmitting the monitoring signal S1. Next, at 810, the LBDC 718 checksto see if the primary battery 714 has fallen below the acceptablevoltage threshold. If it has, the alarm sequence is initiated at 828, ifnot, then the transmission sequence continues.

The transmission sequence continues at 812 with the initiation of thetransmission timing loop. The microcontroller 702 includes or isconnected to a transmission timer, which is set to the time interval“ttmax.” The time interval “ttmax” is the time period between monitoringsignal S1 transmission pulses, assuming no disable signal S2 is receivedin the interim. To allow for the portable unit 30 to be reset/disabledbefore the portable unit alarm is inadvertently activated, and giventhat the maximum allowed time period between reception of monitoringsignal S1 transmission pulses by the portable unit receiver is “trmax,”the time interval “ttmax” is preferably much less than the time interval“trmax.” For instance, if the time interval “trmax” is set to about 7minutes, then the time interval “ttmax” could be set to about 1 minute.Of course, other time intervals can be used with good results.

Next, at 814 the transmission timer time “tt” decrements by “dt,” anddoes so each time through the transmit timing loop. The decrement oftime “dt” may be chosen to calibrate the timer cycle timing to realtime. At 816, the microcontroller 702 checks to see if logical bit T1=1.If the active signal S3 is still being received by the transceiver 704from the detector assembly transmitter 504, indicating that the detectorassembly sensor 22 still detects a child in the car seat 12 and that thecar seat is still within the first proximity range of the base unit 30,then T1=1. If T1=1, then the transmit timing loop continues. If not,then T1=0, and the disable sequence begins at 822.

At 818, if the monitoring signal S1 transmission time interval “ttmax”has not elapsed, then at 814 the transmission timer time “tt” againdecrements by “dt,” with this timing sub-loop continuing until the timeinterval “ttmax” elapses. If the monitoring signal S1 transmission timeinterval “ttmax” has elapsed, then at 820 the medium-range monitoringsignal S1 is transmitted by the transceiver 704 over the secondpredetermined proximity range, and the transmission timing loop is resetand restarted at 812.

If at 816 the active signal S3 reception ceases, indicating that thedetector assembly 20 is beyond the first proximity range of the baseunit 40, that the child is no longer in the car seat 12, or both, thenthe disable sequence begins at 822. In the disable sequence, thetransceiver transmits the disable S2 signal to disable the portableunit, assuming it is within range. Accordingly, in order to avoid falsealarms, the transceiver 704 sends the disable signal S2 over a thirdpredetermined proximity range that is greater than the secondpredetermined proximity range. Then at 824 the indicators 36 arereturned to the standby state. And at 826 the system 700 waits for apredetermined time delay “td” to allow time for any erratic activesignals S3 from the sensor 22 during removal of the child from the carseat 12. Then the system 700 returns to the standby mode at 802.

If at 810 the LBDC 718 determined that the primary battery 714 power waslow, then at 828 the alarm sequence is initiated. In the alarm sequence,the alarm 34 is turned on, then at 830 the LBDC 718 checks the voltageof the primary batteries 714. If the primary batteries 714 have beenreplaced or recharged so that the voltage is now above the minimumacceptable threshold, then the alarm 34 is turned off and the alarmsequence is ended. If not, then the alarm loop continues.

Upon the termination of the disable sequence from 826, and upon thetermination of the alarm sequence from 830 (if it was activated), thesystem 700 is returned to the standby loop at 802. The operationalprocess flow 800 of the system 500 continues in this way, awaiting thenext time the active signal S3 is received by the transceiver 704.

FIG. 9 shows the communication and control system 900 for the portableunit 40. The the portable unit 40 receives from the base unit 30 thesecond proximity-sensitive indication that the sensor 22 is activated bya child in the car seat 12, but only receives the second indication whenthe portable unit 40 and the base unit 30 are close together within thesecond predetermined proximity range. If the child seat 12 is occupiedand is within the first proximity range of base unit 30 and the portableunit 40 is moved beyond the second proximity range of the base unit 30,then the portable unit alarm is activated to notify the caretaker he orshe is about to leave the child in the car. This alarm activation may beprovided by a variety of different systems 900 implementing a variety ofdifferent schemes.

In the first exemplary embodiment, the communication and control system900 includes the disable switch 48, a microcontroller 902, a receiver904, an antenna 906, and various output and power supply components. Theoutput and power supply components include the acoustic transducer 44such as an alarm speaker or piezoelectric buzzer, the indicator lightssuch as LEDs 46, amplifiers 912 for the acoustic transducer 44 and theLEDs 46, a primary power source 914 such as one or more batteries, abackup power source 916 such as one or more batteries, and a low batterydetection circuit (LBDC) 918.

The manual disable switch 48 is a toggle switch, pushbutton, or otherconventional switch that is operated by the user to disable the system10 if the need arises. Such instances might include when a parentintentionally leaves a child in the car with another adult or an oldersibling, when the parent takes the keys out of the ignition to pump andpay for gas with the child in the car, and so forth. The disable switchcan be provided by, for example, a momentary switch, the momentarydepression of which connects the microcontroller 902 to ground todisable the portable unit 40. Alternatively, the disable switch 48 maybe provided in the base unit 30, configured in other ways to disable thesystem 10, or both.

The microcontroller 902 implements the combinational and sequentialfunctions that control the timing and states of the output components(e.g., alarm 44, LEDs 46, etc.) based on the input components (e.g.,disable switch 48, receiver 904, LBDC 918, etc.). The receiver 904converts the modulated, analog, low-magnitude monitoring and disablesignals S1 and S2 received on the antenna 906 from the base unittransceiver 704 to demodulated, buffered, logical voltage signals readby the microcontroller 902. The portable unit receiver 904 receives themonitoring signal S1 from the base unit transceiver 704 only within thesecond predetermined proximity range. But it does so if and only if thechild is detected by the sensor 22 in the car seat 12 and the detectorassembly 20 is within the first predetermined proximity range of thebase unit 30. If the base unit 30 and the detector assembly 20 are notwithin the first predetermined proximity range and/or the child is nolonger detected by the sensor 22 in the car seat 12, then the portableunit receiver 904 instead receives the disable signal S2 from theportable base unit transceiver 704, and the system 10 becomes disabled.

In addition, the microcontroller 902 sends electrical signals to theacoustic transducer 44, the LED indicator lights 46, and/or other outputcomponents. The acoustic transducer 44 converts the electrical signal toan audible sound and the LED indicator lights 46 are illuminated whenactivated. Amplifiers 912 are provided, if needed, to convert (buffer) alow-power logical signal to a powered signal sufficient to drive thealarm speaker 44 or the LEDs 46. Upon receiving an electrical signalfrom the microcontroller 902, one of the LEDs 46 indicates the off-state(LED off), on-state (LED on), and low battery state (LED blinking). Uponreceiving another electrical signal from the microcontroller 902, thealarm speaker 44 sounds to indicate that the batteries are low.

The primary battery 914 delivers power to all active components exceptthe LBDC 918, which is powered by the backup battery 916. The batteries914 and 916 may be consist of single or multiple power cells in seriesor parallel, may be provided by conventional AA, D-cell, or otherbatteries, depending on operational lifetime and power requirements. Inthe present embodiment, the power requirements are based primarily onthe loudness or other intensity characteristic of the alarm 44, and onvery low standby current (<1 mA).

In addition, the LBDC 918 measures the power (e.g., via voltage)remaining in the primary battery 914 and outputs a logical value to themicrocontroller 902 to indicate if the battery voltage is above or belowa predefined “low battery” threshold voltage. If the primary battery is“low” then the microcontroller 902 sends the signals to sound thespeaker alarm 44 and to blink the LED 46, as described above. The backupbatteries 916 can then be used to operate the system 900, allowing sometime for the user to replace or recharge the batteries 914 and 916.

Referring additionally to FIG. 10, there is shown the operationalprocess flow 1000 of the communication and control system 900 of theportable unit 40. At 1002, in the standby mode, the receiver 904 merelywaits, in a standby loop, to be activated by its receiving of themonitoring signal S1. In this mode, at 1004, if the receiver 904 detectsthe monitoring signal S1 from the transceiver 704, logical bit R1 is setto “1.”When this occurs, the standby loop is broken and the portableunit 40 becomes active and the reception timing sequence begins. If not,then the standby loop continues.

At 1006, the reception sequence begins. First, one of the LED indicators46 is turned on. The state of the indicator light 46 (steady orblinking) is determined by the LBDC 918 and is controlled by themicrocontroller 902. Then at 1008, the LBDC 918 checks to see if theprimary battery 914 has fallen below the acceptable voltage threshold.If it has, the alarm sequence is initiated at 1024, if not, then thereception sequence continues.

The reception sequence continues at 1010 with the initiation of thereception timing loop. To start the reception timing loop, logical bitsR1 and R2 are set to “0” and “1,”respectively. Logical bits R1 and R2are the flags that reset or end the subsequent loops if the monitoringsignal S1 or the disable signal S2 is received from the transceiver 704or the disable switch 48 is operated. Accordingly, reception of themonitoring signal S1 resets R1=1. And reception of the disable signal S2or operation of the disable switch 48 sets R2=0.

In addition, the microcontroller 902 includes or is connected to areception timer, which is set to the time interval “trmax.” The timeinterval “trmax” is the maximum allowed time period between reception ofmonitoring signal S1 pulses, assuming no disable signal S2 is receivedin the interim. As mentioned above, to allow for the portable unit 30 tobe reset/disabled before the portable unit alarm 44 is inadvertentlyactivated, the monitoring signal S1 transmission time interval “ttmax”is preferably much less than the time interval “trmax.” Thus, settingthe time interval “ttmax” to about 1 minute and the time interval“trmax” to about 7 minutes provides good results. Of course, other timeintervals can be used with similarly good results.

Next, at 1012 the reception timer time “tr” decrements by “dt” each timethrough the reception timing loop. The decrement of time “dt” may bechosen to calibrate the timer cycle timing to real time.

Then at 1014, the microcontroller 902 checks to see if the logical bitR2=1. The logical bit R2, initially set to “1,” is changed to “0” uponreception of the disable signal S2 or upon operation of the disableswitch 48. So if the logical bit R2 is still set to “1,” then the sensor22 still detects the child in the car seat 12, the detector assembly 20is still within the first proximity range of the base unit 30, and theuser has not operated the manual disable switch 48. In this case, thereception timing loop continues. If not, and the logical bit R2 has beenchanged to “0,” then the system 900 returns to the standby mode and hasbeen effectively disabled.

At 1016 the reception timing loop continues from 1014. Themicrocontroller 902 checks to see if the logical bit R1=1. The logicalbit R1, initially set to “0,” is changed to “1” upon reception of themonitoring signal S1. So if the logical bit R1 has been changed to “1,”then the portable unit 40 is within the second proximity range of thebase unit 30 and the reception timing loop continues at 1010. If not,and the logical bit R1 is still set to “0,” then the reception timingloop continues.

At 1018 the reception timing loop continues from 1016. Themicrocontroller 902 checks to see if the maximum allowed time “trmax”has elapsed. If it has, that is, if the reception timer time “tr” hasdecremented from “trmax” all the way down to “0” without a monitoringsignal S1 being received, then the alarm sequence begins at 1024. Thisis the sequence for operating the alarm 44 to warn the caretaker that heor she is about to leave the child in the vehicle. If the maximumallowed time “trmax” has not elapsed, and time remains before thereception timer time “tr” decrements to “0,” then the reception timingloop continues.

At 1020 the reception timing loop continues from 1018. Themicrocontroller 902 checks to see if the reception timer time “tr” hasdecremented down to a warning time “trw.” The warning time “trw” is setto be less than the maximum allowed time “trmax” and more than zero, sothat as the timer approaches zero the alarm 44 sounds a warning. Thewarning can be a short chirping sound every 30 seconds or another typeof alert with a lower intensity than the full alarm. Thus, if thereception timer time “tr” has not elapsed down to the warning time“trw,” then it continues to decrement at 1012. But if the receptiontimer time “tr” has decremented down past the warning time “trw,” thenat 1022 the warning timer begins (this timing loop resides within themicrocontroller and is not explicitly shown) and the loop continues at1012.

At 1024, the alarm sequence begins from 1010 (low battery) or from 1018(“trmax” elapsed). The alarm may have multiple settings for producingdistinct sounds for the conditions of low battery and “trmax” elapsed(child in left car). Also, the warning for the “trw” elapsed state maybe provided by the same alarm 44. In the alarm sequence, the alarm 44 isturned on and remains on until at 1026 the primary batteries 914 arereplaced or recharged (when activated due to a low battery condition),or until the logical bit R2 is changed to “0” responsive to operation ofthe disable switch 48 or detection of the disable signal S2 (whenactivated due to “trmax” elapsed).

Upon disablement of the system 1000 at 1026 or at 1014, the indicator 46is turned off and the system 1000 is returned to the standby loop at1002. The operational process flow 1000 of the system 900 continues inthis way, awaiting the next time the monitoring signal S1 is received bythe receiver 904.

In the first exemplary embodiment just described, the monitoring andalarm system 10 is provided as an add-on kit for use with an existingchild seat 12. To install the system 10, the sensor mat 22 of thedetector assembly 20 is placed on the seat portion of the child seat 12,the base unit 30 is mounted to or in the proximity of the child seat,and the portable unit keychain fob 40 is connected to the user'skeychain. The base unit 30 may be mounted to the vehicle sun visor bythe clip 38 or another conventional fastener, to the base of the childseat 12 by hook-and-loop fasteners, adhesive strips, screws, or otherconventional fasteners, or to another component of the vehicle of childseat.

For this and other embodiments of the invention, the detector assembly20, the base unit 30, and the portable unit keychain fob 40 can beprovided separately as replacement parts for use with an existingsystem. In this way, if a person loses his or her keys (and the fob 40)or drops and damages the base unit 30, or if the infant repeatedly soilsthe sensor mat 22, then the user can purchase only the neededreplacement component or components.

In addition, the system 10 can be factory built into new vehicles, withthe detector assembly 20 manufactured into the back seat, the base unit30 built into or mountable onto the sun visor, the dash board, oranother vehicle component, and the portable unit keychain fob 40provided with the new vehicle keys. In this arrangement, the sensor 22of the detector assembly 20 can be calibrated to account for the weightof the car seat 12 on it, so that additional weight would indicate thepresence of the child.

Turning now to FIG. 11, there is shown a second exemplary embodimentaccording to the invention, referred to as the child-proximitymonitoring and alarm system 1100. In this embodiment, the system 1100 issimplified for use with a unitary child seat 1112 in which the shell isnot detachable from the base. Of course, the same system 1100 can beused with two-piece or other types of car seats 1112, if so desired.

For use with a unitary child seat 1112, there is no need for theproximity-sensitive indication of whether the shell is mounted to or inproximity to the base. So the detector assembly 1120 includes the sensor1122 and the transmitter 1102 that transmits to the portable unit 1140the proximity-sensitive indication that the car seat 12 is occupied. Thetransmitter 1102 may be mounted to the base of the car seat 12 orelsewhere, and electrically communicates with the sensor 1122 by wiresor wirelessly. And the portable unit 1140 includes the alarm 1144 andthe receiver that receives the proximity-sensitive indication from thedetector assembly transmitter 1102.

In this way, the detector assembly 20 and the base unit 30 of the firstembodiment are essentially combined into a single functional unit, whichpermits the elimination of a number of components in the simplifiedsystem 1100. Components that can be eliminated include the receiverfunction of the base unit 30, the transmitter function of the detectorassembly 20, and redundant components such as microcontrollers,antennas, indicator lights, alarms, amplifiers, and batteries. Thetransmitter function of the base unit 30 is provided in the simplifiedsystem 1100 by the transmitter 1102 of the detector assembly 1120.

Turning now to FIG. 12, there is shown a third exemplary embodimentaccording to the invention, referred to as the child-proximitymonitoring and alarm system 1200. In this embodiment, the system 1200 ismade and sold integrally with the child seat 1212. Thus, the sensor mat1222 is built into the seat portion of the child seat 1212, immediatelyon its top surface or embedded into the seat cushion. Similarly, thebase unit 1230 is built into the base of the child seat 1212 so that itis unobtrusive, in a housing integrally formed with the base or in aseparate housing mounted to it. Of course, the components of the system1200 can be built into other parts of the child seat 1212, as may bedesired for different child seats. And although the system 1200 is shownhaving components similar to those of the first exemplary embodiment,the system can be provided with components similar to those of thesecond or other embodiments.

Turning now to FIGS. 13A and 13B, there is shown a portion of a fourthexemplary embodiment according to the invention, referred to as thechild-proximity monitoring and alarm system 1300. In this embodiment,the system 1300 is provided integrally with the child seat like thethird exemplary embodiment, and it includes the major components of thefirst or second exemplary embodiments, except that a different sensor1320 is provided. Instead of the weight-sensitive mat, the sensor 1320is provided by a switch configured for determining if a seat belt 1302of the child seat 1312 is connected. The switch 1320 includes the maleand female connectors 1304 and 1306 of the seat belt 1302. A pushbutton1308 is mounted in the opening of the female connector 1306 so that thepushbutton is depressed by the male connector 1304 when inserted intothe female connector. Alternatively, the male and female connectors 1304and 1306 can be configured so that when they are connected they contactand conduct electricity, or other open/close switch configurations canbe provided. Also, the switch 1320 includes a jack 1310 for connectingwires between the switch and the transmitter of the detector assembly.Alternatively, the transmitter can be positioned immediately adjacent orintegrally with the female end connector 1306 so that the jack is notneeded.

The switch 1320 is “open” when the seat belt connectors 1304 and 1306are disconnected, indicating that the child seat 1312 is unoccupied. Andthe switch 1320 is “closed” when the seat belt connectors 1304 and 1306are connected, indicating that the child seat 1312 is occupied.Accordingly, the transmitter sends the active signal S3 only when theseat belt connectors 1304 and 1306 are connected. Since most parentskeep the seat belt 1302 disconnected so they can more easily put theirchild in the car seat 1312, and always connect the seat belt when thechild is in the child seat, this arrangement provides an appropriatechild-sensing indication.

Turning now to FIG. 14, there is shown a portion of a fifth exemplaryembodiment according to the invention, referred to as thechild-proximity monitoring and alarm system 1400. In this embodiment,the system 1400 is provided integrally with the child seat like thethird exemplary embodiment, and it includes the major components of thesecond exemplary embodiment. In addition, a second sensor 1402determines if the detachable shell 1412 a of the car seat 1412 ismounted to the base 1412 b, and communicates this via the transmitter1404 of the detector assembly 1420 to the portable unit (not shown). Thesecond sensor 1402 may be provided by a pair of mating contacts mountedto the base 1412 b and the shell 1412 a, a pushbutton mounted to theunderside of the shell 1412 a that is depressed by the base 1412 b whenthe shell is mounted to the base, or by other conventional switchingmechanisms.

The control system of the detector assembly 1420 and/or the portableunit activates the corresponding alarm to alert the caretaker if theshell 1412 a is removed from the base 1412 b, based on input from thesecond sensor 1402, while the child seat 1412 is occupied, based oninput from the sensor 1422 of the detector assembly 1420. In this way,the system 1400 can be used with two-piece car seats 1412 withoutincluding the base unit of the first embodiment.

In addition, a number of other embodiments of the invention may beprovided. In one alternative embodiment, a child-proximity andmonitoring system is provided with two portable unit keychain fobs foruse with one base unit, so that either parent can drive the car with thechild seat in it. In another alternative embodiment, the system isprovided with multiple base units operable with a single keychain fob,so that a parent with more than one child can use multiple child seatsand only need one fob. And in still another embodiment, the system isprovided with two (or more) keychain fobs for use with two (or more)base units, so that either parent can use their fob with either of theircars, regardless of which of the child seats is in that car. Of course,other variations of the number of the major components included in thesystem can be provided.

In yet another alternative embodiment, the sequence ofproximity-sensitive communications is from base unit to detectorassembly to portable unit, instead of from detector assembly to baseunit to portable unit. This is somewhat similar to the configurationprovided in the fifth exemplary embodiment. And in other embodiments thesystem is adapted for use in monitoring the presence of a pet in avehicle and providing an alarm to prevent leaving the pet in the car. Inone such embodiment, the sensor is provided, for example, by aweight-sensitive mat in a pet carrier. In another such embodiment thecarrier is the vehicle itself and the sensor determines whether the petis in it by, for example, a proximity indication scheme implemented byadditionally providing a transmitter, transceiver, or other deviceattached to the pet collar. It will be understood that the system can beadapted for use in proximity-sensitive monitoring of other objects underother circumstances.

Accordingly, the present invention provides a child-proximity monitoringand alarm system that notifies a parent or other caretaker when about tounintentionally leave a child in a vehicle. Advantageously, the keychainfob or other portable unit has proximity-sensitive capabilities and analarm for alerting the parent when leaving the proximity of the carwhile the child is still in the car seat. Furthermore, to avoid falsealarms when used with two-piece car seats, the system is implementedwith a base unit for relaying proximity-sensitive communications fromthe detector assembly to the keychain fob. In addition, the system canbe provided as an add-on kit for use with an existing child car seat orit can be built into and provided with a new child seat, whether thechild seat is the unitary or two-piece type. Moreover, the variousembodiments of the invention are efficient to manufacture, install, anduse.

In the embodiments described above and in the following claims, thewords “a,” “an,” and “one” are not intended to mean “only one” but canalso mean any number greater than one. Similarly, plural terms aresometimes used for convenience and are not necessarily intended to mean“more than one” but can also mean just “one.” While the invention hasbeen shown and described in exemplary forms, it will be apparent tothose skilled in the art that many modifications, additions, anddeletions can be made therein without departing from the spirit andscope of the invention as set forth in the following claims.

1. An object-proximity monitoring and alarm system for use with anobject carrier, comprising: at least one sensor adapted to determinewhether the object carrier is occupied; a main transmitter incommunication with the sensor; and a portable unit including a receiverand an alarm, wherein the main transmitter is operable to communicate tothe portable unit receiver whether the object carrier is occupied basedon input from the sensor, and the portable unit is operable to activatethe alarm if the object carrier is occupied and the receiver is removedbeyond a first predetermined proximity range of the main transmitter. 2.The object-proximity monitoring and alarm system of claim 1, wherein thesensor comprises a weight-sensitive mat.
 3. The object-proximitymonitoring and alarm system of claim 1, wherein the portable unitcomprises a keychain fob housing the alarm and the receiver.
 4. Theobject-proximity monitoring and alarm system of claim 1, wherein: themain transmitter is operable to intermittently transmit a firstelectromagnetic signal responsive to the input from the sensor that theobject carrier is occupied, and to transmit a second electromagneticsignal responsive to the input from the sensor that the object carrierceases to be occupied; and the portable unit is operable to receive thefirst and second electromagnetic signals, and to activate the alarm ifmore than a predetermined length of time passes between successivereceptions of the first electromagnetic signal, unless one of the secondelectromagnetic signals is received in the predetermined length of time.5. The object-proximity monitoring and alarm system of claim 4, whereinthe main transmitter is operable to transmit the first signal with astrength that is receivable by the portable unit receiver only withinthe first predetermined proximity range so that the alarm is activatedif the portable unit is moved beyond the first proximity range of themain transmitter.
 6. The object-proximity monitoring and alarm system ofclaim 5, further comprising: a detector assembly including the sensorand a second transmitter operable to transmit a third electromagneticsignal with a strength that is receivable only within a secondpredetermined proximity range; and a base unit including a transceivercomprising the main transmitter and a second receiver, wherein theportable unit is operable to activate the alarm only if the third signalis being received by the second receiver of the transceiver so that theportable unit alarm can be activated only if the base unit is within thesecond proximity range of the detector assembly.
 7. The object-proximitymonitoring and alarm system of claim 1, further comprising: atransceiver including the main transmitter and a second receiver; and asecond transmitter operable to transmit a third electromagnetic signal,wherein the portable unit is operable to activate the alarm only if thethird signal is being received by the second receiver of thetransceiver.
 8. The object-proximity monitoring and alarm system ofclaim 1, further comprising: a detector assembly including the sensor;and a base unit in a proximity-sensitive relationship with the detectorassembly, wherein the portable unit is operable to activate the alarmonly if the detector assembly and the portable unit are within apredetermined proximity range of each other.
 9. The object-proximitymonitoring and alarm system of claim 8, wherein the base unit includes atransceiver comprising the main transmitter and a second receiver, thedetector assembly includes a second transmitter operable to transmit athird electromagnetic signal, and the portable unit is operable toactivate the alarm only if the third signal is being received by thesecond receiver of the transceiver.
 10. The object-proximity monitoringand alarm system of claim 9, wherein the second transmitter of thedetector assembly is operable to transmit the third electromagneticsignal responsive to the input from the sensor that the object carrieris occupied.
 11. The object-proximity monitoring and alarm system ofclaim 9, wherein the second transmitter of the detector assembly isoperable to transmit the third electromagnetic signal with a strengththat is receivable by the second receiver of the base unit transceiveronly within a second predetermined proximity range so that the portableunit is operable to activate the alarm only if the base unit is withinthe second proximity range of the detector assembly.
 12. Theobject-proximity monitoring and alarm system of claim 1 in combinationwith the object carrier.
 13. The object-proximity monitoring and alarmsystem of claim 12, wherein the object carrier comprises a child seatsecurable within a vehicle.
 14. The object-proximity monitoring andalarm system of claim 13, wherein the child seat comprises a base and ashell detachably mounted to the base, and further comprising at leastone second sensor adapted to determine if the shell is mounted to thebase, wherein the portable unit is operable to activate the alarm onlyupon a determination by the second sensor that the shell is mounted tothe base.
 15. The object-proximity monitoring and alarm system of claim13, wherein the sensor comprises a switch configured for determining ifa seat belt of the child seat is connected.
 16. A child-proximitymonitoring and alarm system for use with a child seat securable within avehicle, comprising: a detector assembly including a sensor and a secondtransmitter, wherein the sensor includes a weight-sensitive mat adaptedto determine whether the child seat is occupied and the secondtransmitter is operable to transmit a first indication that the childseat is occupied responsive to input from the sensor; a base unitincluding a transceiver operable to receive the first indication thatthe child seat is occupied and, responsive thereto, to transmit a secondproximity-sensitive indication that the child seat is occupied; and akeychain fob housing an alarm and a receiver operable to receive thesecond proximity-sensitive indication that the child seat is occupiedand to activate the alarm if the fob receiver is removed beyond a firstpredetermined proximity range of the main transmitter while the childseat is occupied, wherein the base unit is configured to transmit thefirst proximity-sensitive indication that the child seat is occupiedonly if the child seat is within a second predetermined proximity rangeof the base unit.
 17. The child-proximity monitoring and alarm system ofclaim 16, wherein the detector assembly second transmitter is operableto transmit a third electromagnetic signal responsive to the input fromthe sensor that the child seat is occupied, and the base unittransceiver is operable to transmit the first proximity-sensitiveindication that the child seat is occupied only if the thirdelectromagnetic signal is being received.
 18. The child-proximitymonitoring and alarm system of claim 17, wherein the detector assemblysecond transmitter is operable to transmit the third electromagneticsignal with a strength that is receivable by the transceiver only withinthe second predetermined proximity range so that the keychain fobreceiver is operable to activate the alarm only if the base unit iswithin the second proximity range of the detector assembly.
 19. Thechild-proximity monitoring and alarm system of claim 17, wherein: thetransceiver is operable to intermittently transmit a firstelectromagnetic signal if the third signal is being received and totransmit a second electromagnetic signal if the third signal is notbeing received; and the keychain fob receiver is operable to receive thefirst and second electromagnetic signals and to activate the alarm ifmore than a predetermined length of time passes between successivereceptions of the first electromagnetic signal, unless one of the secondelectromagnetic signals is received in the interim.
 20. Thechild-proximity monitoring and alarm system of claim 19, wherein thetransceiver is operable to transmit the first signal with a strengththat is receivable by the keychain fob receiver only within a firstpredetermined proximity range so that the alarm is activated if thekeychain fob is moved beyond the first proximity range of the base unit.21. The child-proximity monitoring and alarm system of claim 16 incombination with the child seat.
 22. The child-proximity monitoring andalarm system of claim 21, wherein the child seat comprises a base and ashell detachable from the base, and the sensor is included in orpositionable on the child seat shell and the base unit is included in orpositionable in proximity to the child seat base.
 23. A child-proximitymonitoring and alarm system for use with a child seat securable within avehicle, comprising: at least one sensor including a weight-sensitivemat adapted to determine whether the child seat is occupied; a maintransmitter in communication with the sensor and operable tointermittently transmit a first electromagnetic signal responsive toinput from the sensor that the child seat is occupied, and to transmit asecond electromagnetic signal responsive to input from the sensor thatthe child seat ceases to be occupied; and a keychain fob housing analarm and a receiver operable to receive the first and secondelectromagnetic signals and to activate the alarm if more than apredetermined length of time passes between successive receptions of thefirst electromagnetic signal, unless one of the second electromagneticsignals is received in the interim, wherein the main transmitter isoperable to transmit the first signal with a strength that is receivableby the keychain fob receiver only within a first predetermined proximityrange so that the alarm is activated if the keychain fob is moved beyondthe first proximity range of the main transmitter.
 24. Thechild-proximity monitoring and alarm system of claim 23 in combinationwith the child seat.
 25. The child-proximity monitoring and alarm systemof claim 24, wherein the child seat comprises a base and a shelldetachable from the base, the sensor is included in or positionable onthe child seat shell, and the main transmitter is included in orpositionable in proximity to the child seat base.
 26. A portable unitfor use in a child-proximity monitoring and alarm system used with achild seat securable within a vehicle, the monitoring and alarm systemincluding at least one sensor adapted to determine whether the childseat is occupied and a main transmitter operable to transmit aproximity-sensitive indication that the child seat is occupied based oninput from the sensor, the portable unit comprising: a receiver operableto receive from the main transmitter the proximity-sensitive indicationthat the child seat is occupied; and an alarm operable to activateresponsive to the receipt of the proximity-sensitive indication that thechild seat is occupied if the portable unit receiver is removed beyond afirst predetermined proximity range of the main transmitter.
 27. Theportable unit of claim 26, wherein: the receiver is operable to receivefrom the main transmitter intermittent transmissions of a firstelectromagnetic signal responsive to the input from the sensor that thechild seat is occupied, and to receive from the transmitter a secondelectromagnetic signal responsive to the input from the sensor that thechild seat ceases to be occupied; and the alarm is operable to activateif more than a predetermined length of time passes between successivereceptions of the first electromagnetic signal, unless one of the secondelectromagnetic signals is received in the interim.
 28. The portableunit of claim 26, wherein the portable unit comprises a keychain fob.29. A base unit for use in a child-proximity monitoring and alarm systemused with a child seat securable within a vehicle, the monitoring andalarm system including a sensor, a second transmitter operable totransmit a first indication that the child seat is occupied based oninput from the sensor, and a portable unit comprising a receiver and analarm, the base unit comprising: a transceiver operable to receive thefirst indication from the second transmitter that the child seat isoccupied based on the input from the sensor and, responsive thereto, totransmit a second proximity-sensitive indication that the child seat isoccupied that is receivable by the portable unit receiver only within afirst predetermined proximity range, wherein the alarm is activated ifthe portable unit is removed beyond the first predetermined proximityrange of the transceiver.
 30. The base unit of claim 29, wherein thetransceiver is operable to receive from the second transmitter a thirdelectromagnetic signal responsive to the input from the sensor that thechild seat is occupied, and to intermittently transmit a firstelectromagnetic signal if the third signal is being received and totransmit a second electromagnetic signal if the third signal is notbeing received, wherein the portable unit receiver receives the firstand second electromagnetic signals and activates the alarm if more thana predetermined length of time passes between successive receptions ofthe first electromagnetic signal, unless one of the secondelectromagnetic signals is received in the interim.
 31. The base unit ofclaim 30, wherein the transceiver is operable to receive the thirdelectromagnetic signal only within a second predetermined proximityrange of the second transmitter and to transmit the first signal with astrength that is receivable by the portable unit receiver only withinthe first predetermined proximity range of the of the transceiver sothat the alarm can be activated if the portable unit is moved beyond thefirst proximity range of the transceiver but only if the transceiverremains within the second proximity range of the second transmitter. 32.A detector assembly for use in a child-proximity monitoring and alarmsystem used with a child seat securable within a vehicle, the monitoringand alarm system including a portable unit having a receiver operable toreceive a proximity-sensitive indication that the child seat is occupiedand an alarm operable to activate responsive thereto, the detectorassembly comprising: at least one sensor adapted to determine whetherthe child seat is occupied; and a transmitter operable to communicate tothe portable unit receiver only within a first predetermined proximityrange the proximity-sensitive indication that the child seat is occupiedbased on input from the sensor, wherein the alarm is activated if theportable unit is removed beyond the first predetermined proximity rangeof the transmitter.
 33. The detector assembly of claim 32, wherein thetransmitter is operable to transmit intermittent transmissions of afirst electromagnetic signal responsive to the input from the sensorthat the child seat is occupied, and to transmit a secondelectromagnetic signal responsive to the input from the sensor that thechild seat ceases to be occupied, wherein the alarm activates if morethan a predetermined length of time passes between successive receptionsof the first electromagnetic signal, unless one of the secondelectromagnetic signals is received in the interim.
 34. The detectorassembly of claim 32, wherein the child-proximity monitoring and alarmsystem further includes a base unit comprising a transceiver, whereinthe transmitter is operable to transmit a third electromagnetic signalresponsive to the input from the sensor that the child seat is occupiedand the third signal is receivable by the transceiver only within thefirst predetermined proximity range, wherein the transceiver transmitsintermittent transmissions of a first electromagnetic signal if thethird signal is received and transmits a second electromagnetic signalif the third signal is not received, and the alarm activates if morethan a predetermined length of time passes between successive receptionsof the first electromagnetic signal, unless one of the secondelectromagnetic signals is received in the interim.
 35. The detectorassembly of claim 32, wherein the sensor comprises a weight-sensitivemat.
 36. An object-proximity monitoring and alarm system for use with anobject carrier, comprising: at least one sensor adapted to determinewhether the object carrier is occupied; a main transmitter incommunication with the sensor; and a portable unit including a receiverand an alarm, wherein the main transmitter is operable to communicate atleast two different electromagnetic signals to the portable unitreceiver based on input from the sensor, the portable unit is operableto determine whether the object carrier is occupied by interpreting theat least two different electromagnetic signals, and the portable unit isfurther operable to activate the alarm if the object carrier is occupiedand the receiver is removed beyond a first predetermined proximity rangeof the main transmitter by interpreting the at least two differentelectromagnetic signals.